Vietnamese Transport Minister Dinh La Thang launched Thursday an attempt to sell his plan to construct a multibillion-dollar airport in a southern province with a lower investment estimate than the previous feasibility report unveiled four months ago, but lawmakers did not seem convinced.

Minister Thang told a lawmaking National Assembly session in a report in late October last year that Long Thanh International Airport, to be built in the eponymous district of Dong Nai Province, would consume

US$18.7 billion worth of investment over three construction phases ending by 2030.

The first phase will require an estimated $7.8 billion, while the respective capital needed for the next two phases is $3.8 billion and $7 billion.

But as he addressed the National Assembly Standing Committee in Hanoi yesterday, Thang said the new estimate for the project, which raised concerns over its huge investment and necessity, is $2.9 billion lower than previously estimated.

“The new estimate for the project is $15.8 billion, with $5.2 billion allocated for the first phase,” Thang told lawmakers.

The new figure was calculated with reference to “projects of similar scales that have been and are being implemented” in the region and the world, according to the transport minister.

The previous feasibility report said Long Thanh airport will span an area of 5,000 hectares, but Thang said the project will now need only 2,750 hectares.

The area does not include a 1,050-hectare land plot zoned for military purposes, and 1,200 hectares for the construction of other support units and an aviation industrial park.

Long Thanh District is about 50km east of Ho Chi Minh City.

The headline-grabbing proposed airport is expected to be able to handle 100 million passengers a year by its last phase.

The transport ministry has tried to show the necessity of building the Long Thanh airport by proving that Ho Chi Minh City-based Tan Son Nhat International Airport will become overloaded in the next two years.

The domestic and international terminals at Tan Son Nhat have a total capacity of 25 million passengers a year, according to the report.

The airport is projected to reach this threshold by 2016 and, from that point on, become overloaded. The airport has been serving 20 million passengers a year since 2013.

Even though the megaproject would now require smaller investment, many lawmakers still greeted the transport minister with tough questions after hearing his new report.

Phung Quoc Hien, chairman of the National Assembly’s Finance and State Budget Committee, wondered whether Long Thanh is the top priority among many other essential public investments at a time when the country is “falling short of capital.”

“The construction of a north to south expressway is crucial for our modernization process, and the Hanoi – Ho Chi Minh City railway is now centuries-old,” he said.

“So which priority should we set [for these projects]… Is the [Long Thanh] airport really necessary now?”

Hien also expressed concerns about the financial mechanism to fund the project, adding the first phase of the project could cost the state budget as much as VND40.1 trillion ($1.87 billion).

“What is the chance of recouping investment for such a megaproject?” he challenged.

In response, Minister Thang said the government-backed planning for the Vietnamese transport sector from now to 2020 and 2030 has prioritized Long Thanh airport, and the state coffers would only account for 30 percent of the total investment.

As for the economic effectiveness of the project, Thang asserted that “all of the recent airport projects are operating at a gain,” and “none of them have gone bankrupt.”

In concluding the meeting, National Assembly deputy chairwoman Nguyen Thi Kim Ngan ordered that the transport ministry work out on a more detailed report, which should explain clearly how the estimate could be lowered by nearly $3 billion.